Researchers, especially in the biotech field, frequently need to know if a bioreactor of a specific setup will produce the desired final product.
Due to an occasionally high particulate content of a bioreactor sample, the sample is currently clarified in the lab by multiple centrifugations. Subsequently, in order to simulate a sterile final product, the supernatant is filtered in a separate device. At this step it is possible to use a 0.22 μm filter membrane (i.e. a MILLEX™ 0.22 μm membrane from MILLIPORE) combined with a syringe. Assuming that the filter membrane is not clogging, the maximum processed volume is the volume of the syringe which is typically 50 ml.
Furthermore, this process is a multi-step protocol where the personnel has to walk several times to the centrifuge and a laminar flow hood, and it is an “open” protocol which increases the risk of contamination of the sample.
One current approach to reduce the number of steps is co use so called “syringeless filters” commercially available from WHATMAN under the tradenames UNIPREP™ and AUTOVIAL™.
Autovial™ syringeless filters are preassembled filtration devices fox removing particulates from samples. They replace syringe-coupled filtration devices with single, disposable units. These devices are comprised of two parts; a graduated filter barrel and a plunger. The design features an integral filter, built-in air purge and a support stand that protects a recessed slip-luer tip. The devices are available in a 5 ml and 12 ml volume capacity.
The filter is selected according to membrane compatibility with the sample. In practice, the sample is poured into the 5 ml or 12 ml capacity filter barrel. The plunger is inserted into the barrel until the bottom is securely in place; there is a gap of air between the sample and plunger. Then, the tip of the device is placed into the mouth of an autosampler vial or container and the plunger compressed. Filtration begins immediately and, as the plunger is compressed until it reaches the bottom, the membrane is purged with air for maximum sample recovery. For direct instrument injection, a needle is placed on the slip-luer outlet.
UniPrep™ syringeless filters are preassembled filtration devices, too, for the filtration and storage of laboratory samples. These devices include a plunger, filter and vial in one unit. They replace syringe-coupled filtration devices with single, disposable units. These devices consist of two parts: a test tube and a filter-plunger where a membrane is mounted into the tip of the plunger. When the filter plunger is pressed through the liquid placed in the test tube, positive pressure forces the filtrate up into a reservoir of the filter-plunger. The devices can be used to filter only small sample volumes in the range from 1 to 5 ml.
A still further range of products are available under the name Mini-UniPrep™ which is a preassembled filtration device consisting of a 0.4 ml capacity chamber and a plunger. The plunger contains a filtration membrane at one end and a preattached cap/septum at the other. The plunger is pressed through the sample in an outer chamber and positive pressure forces the filtrate into a reservoir of the plunger. Air escapes through a vent hole. The device can be used either individually manually or with a manually operated compressor unit which comprises a manually operated lever that can be pressed on up to 6 samples standing on a base. This device is designed to fit into an autosampler accommodating 12×32 mm vials. Alternatively the septum can be pierced with a needle and the sample drawn off for manual injection into an analyzer.
Filter membranes of such devices are typically made from the following materials depending on the intended sample to be processed: cellulose acetate (CA) (a low nonspecific protein binding and high loading capacity membrane for biological solutions), glass microfiber (GMF) (a depth filter for samples in aqueous or organic solutions), nylon (NYL) (for aqueous and organic samples within a pH range between of 3 to 10), polyethersulfone (PES) (a low non-specific protein binding membrane for samples in aqueous solutions), polypropylene (PP) (a hydrophobic membrane which is resistant to a wide range of organic solvents), polytetrafluorethylene (PTFE) (a Teflon® membrane for samples with >50% organic solvent), polyvinylidene fluoride (PVDF) (a low nonspecific protein binding membrane for samples in aqueous solutions and/or organic solvents).
In order to allow the filtration of difficult samples, the design incorporates a glass fiber prefilter. Although these devices are easy to use they are even more limited by the sample size (i.e. only 12 ml maximum) and are subject to the clogging of the final membrane.
U.S. Pat. No. 5,238,003 discloses a manually operable blood drawing syringe having a barrel with a hollow cylindrical bore with an open rear end and a reduced diameter front end for the attachment of a needle. A pushrod is disposed for slidable movement within the barrel and a disc-shaped plunger or piston is attached to the forward end of the pushrod. A filter which will pass air but is impervious to fluids is disposed between forward and rear perforated plates of the plunger and a sealing flange is disposed around the periphery of the plunger and dimensioned to fit slidingly within the cylindrical bore of the barrel. A flapper seal which is impervious to both gas and fluids is located in abutting contact with the rear face of the plunger and allows air that has passed through the filter in the plunger to escape from an upstream volume into a downstream volume as the pushrod and the plunger move forward in the barrel.
EP-A-0294185 discloses a filtering device for fluids which is similar to the above described Autovial™ syringeless filters. It comprises a barrel with an open end sod a flow discharge end with a nipple that is in communication with the interior volume of the barrel. A plunger is slidable disposed in the barrel through the open end towards the discharge end. A filter is disposed adjacent the barrel inwardly of and adjacent to the discharge nipple. In operation the sample fluid to be filtered is poured into the volume of the barrel so as to be disposed above the filter. The plunger is then inserted into the open end of the barrel and pushed towards the flow discharge end. The sample will have been fully filtered and dispensed from the nipple when the plunger is fully depressed and the forward face of the plunger engages a bottom end of the barrel. This device suffers from the premature clogging of the membrane surface if samples with a larger particulate material load are to be processed.
WO 97/15399 discloses a portable and disposable centrifugal cell separation device for biological fluids like blood. The device comprises a hollow centrifugal processing chamber rotatable about an axis of rotation and having a common axial inlet/outlet port for the fluid to be processed. The processing chamber contains a movable plunger which defines a separation space of variable size and a vacuum/pressure space and being movable to intake the selected quantity of a sample fluid into the separation space via the inlet/outlet port, and to express processed sedimented fluid components after centrifugation from the separation space via the inlet/outlet port. The plunger is moved towards the inlet/outlet port end of the processing chamber by pressurized air introduced into the vacuum/pressure space.